Welcome Samoy: My mom had a Narcissistic Deficiency Dysphoria which required her to be hospitalize. In some ways her being in the hospital was a blessing since what I always thought is now validated. What I'm perplexed about is she says she doesn't remember any of it; which I don't understand.
Sounds like you have had a long history of problems with you mom. Are you able to share some of the main issues over the years? Most of the communication skills and strategy found here should apply to a NPD person, as well as a BPD. Actually, most of the skills are good to learn and use in relationships with people in every day life.
I'm not as familiar with NPD. From what I've read, a Narcissistic Deficiency Dysphoria is a major depression related to the narcissist's depletion of victims or situations to feed their narcissism. Has something changed in your mom's life recently? (a move, loss of a friend of loved one, someone moved, etc.)
Both people with NPD and BPD can have issues with lying. You might find the article at the following link helpful:
Why Do Narcissists and Borderlines Lie So Much?The links below lead to some more resources:BOOK: Stop Caretaking the Borderline or Narcissist
https://bpdfamily.com/message_board/index.php?topic=203887.0Understanding the Narcissistic Family
https://bpdfamily.com/message_board/index.php?topic=108970.0;allIs Your Narcissist the "Vulnerable" or "Grandiose" Type?
www.BPDcentral.com/blog/?Is-Your-Narcissist-the-Vulnerable-or-Grandiose-Type-22